Description (Adapted from Application): An examination of the structures and properties of classical and non-classical nucleic acid base pairs using theoretical methods is proposed. One specific aim of this research is to study the molecular structures and stabilities of the above compounds by ab initio quantum mechanical calculations. Hydrogen-bonding and stacking interactions between classical purine nucleic acid bases and classical pyrimidine nucleic acid bases will be studied, as well as non-classical systems that might increase the catalytic role of RNA and DNA molecules and the fidelity of replications. These studies will predict interaction energies of the WC and reverse-WC pairs of classical and non-classical species and their stacking complexes. Different derivatives of the classical NABs will be examined to gain an understanding of how selected substituents could modify the probability of spontaneous mutations of the parent molecules. The studies are designed to assist experimental studies on the title species by providing theoretical molecular geometries, dipole moments, rotational constants, and vibrational frequencies and intensities. The projects are designed to expose underrepresented minorities to the theory and practice of quantum chemical methods. The development of computer and supercomputer literacy and of the oral and written communicative skills of students will be a major thrust of this research project.